I just read that Amazon rainforest natives traditionally used a unique form of slash & burn farming, cutting small openings first to semi-dry the damp understory, then burned smoldering low fires, resulting in a partially charred ground layer this greatly enriched the impoverished acidic rainforest soil, because it left a layer of organic/fertile Terra Preta = black charcoal soil

this is very different from the usual modern method of slash & burn using chainsaws to remove the high-value trees and much of the canopy then sun dry the soil and then light hot fires to burn off all the vegetation leaving an ASH layer which is mineral-rich but soon washes away leaving sunbaked crusty soil.

I had never heard of the Terra Preta method before, some rainforest farmers do this repeatedly producing soils richer than Kansas topsoil! This is excellent forage/gather/garden management of rainforests, and I wonder if it is practiced elsewhere. I was trained to view all slash & burn (swidden) agriculture negatively, (due to often excessive erosion of topsoil) so I have to revise my views on it.

Superdirt Made Lost Amazon Cities Possible?John Roachfor National Geographic NewsNovember 19, 2008Centuries-old European explorers' tales of lost cities in the Amazon have long been dismissed by scholars, in part because the region is too infertile to feed a sprawling civilization.

But new discoveries support the idea of an ancient Amazonian urban network—and ingeniously engineered soil may have made it all possible.

Now scientists are trying to recreate the recipe for the apparently human-made supersoil, which still covers up to 10 percent of the Amazon Basin. Key ingredients included of dirt, charcoal, pottery, human excrement and other waste.

If recreated, the engineered soil could feed the hungry and may even help fight global warming, experts suggest.

(Interactive map: "The Embattled Amazon.")

Before 1492

Scientists have long thought the river basin's tropical soils were too acidic to grow anything but the hardiest varieties of manioc, a potatolike staple.

But over the past several decades, researchers have discovered tracts of productive terra preta—"dark earth." The human-made soil's chocolaty color contrasts sharply with the region's natural yellowish soils.

Research in the late 1980s was the first to show that charcoal made from slow burns of trees and woody waste is the key ingredient of terra preta.

With the increased level of agriculture made possible by terra preta, ancient Amazonians would have been able to live in one place for long periods of time, said geographer and anthropologist William Woods of the University of Kansas."As a result you get social stratification, hierarchy, intertwined settlement systems, very large scale," added Woods, who studies ancient Amazonian settlements.

"And then," he said, "1492 happens." The arrival of Europeans brought disease and warfare that obliterated the ancient Amazonian civilizations and sent the few survivors deep into the rain forest to live as hunter-gatherers.

"It completely changed their way of living," Woods said.

Magic Soil?

Today scientists are racing to tease apart the terra-preta recipe. The special soil has been touted as a way to restore more sustainable farming to the Amazon, feed the world's hungry, and combat global warming.

The terra-preta charcoal, called biochar, attracts certain fungi and microorganisms.

Those tiny life-forms allow the charcoal to absorb and retain nutrients that keep the soil fertile for hundreds of years, said Woods, whose team is among a few trying to identify the crucial microorganisms.

"The materials that go into the terra preta are just part of the story. The living member of it is much more," he said.

For one thing, the microorganisms break up the charcoal into smaller pieces, creating more surface area for nutrients to cling to, Woods said.

Anti-Global-Warming Weapon?

Soil scientist Johannes Lehmann of Cornell University is also racing to recreate terra preta.

The Amazonian dark soils, he said, are hundreds to thousands of years old, yet to this day they retain their nutrients and carbons, which are held mainly by the charcoal.

This suggests that adding biochar could help other regions of the world with acidic soils to increase agricultural yields.

Plus, Lehmann said, biochar could help reduce the amount of greenhouse gas emissions released into the atmosphere from the burning of wild lands to create new farm fields. (Learn how greenhouse gas emissions may worsen global warming.)

For example, specialized power plants could char agricultural wastes to generate electricity.

The process would "lock" much carbon that would have otherwise escaped into the atmosphere in the biochar. The biochar could then be put underground, in a new form of terra preta, thereby sequestering the carbon for centuries, Lehmann suggests.

Current Amazonian farming relies heavily on slash-and-burn agriculture—razing forests, then burning all of what's left.

By reverting to the ancient slash-and-char method—burning slowly and then mixing the charcoal into the soil—Amazonian carbon dioxide emissions could be cut nearly in half, according to Woods, of the University of Kansas.

With slash-and-burn, he noted, 95 percent of the carbon stored in a tree is emitted to the atmosphere. Slash-and-char emits about 50 percent, he said.

"The rest is put into different forms of black carbon, most of which are chemically inert for long periods of time—thousands of years."

In addition, the technique would allow many farmers to stay sedentary, Woods said.

Because the soil would apparently remain fertile for centuries, "they don't have to cut down the forest constantly and send it up into the atmosphere," he said.
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posted 12. April 201503:26 PM
I learned of it only this week... although I had heard the term previously. I studied internationally at University level tropical forest ecology/soils etc., Slash & burn was almost ALWAYS considered "bad" due to rainfall washing away fertility etc. Deliberate cool charring was never discussed in forest ecology classes with regard to replanting, the focus was more on the forest canopy rather than the soil quality. That was a big omission, but typical of industrial timber/pulp production's effects on Forestry profession.

quote:Originally posted by DD'eDeN:[QB] I learned of it only this week... although I had heard the term previously. I studied internationally at University level tropical forest ecology/soils etc., Slash & burn was almost ALWAYS considered "bad" due to rainfall washing away fertility etc. Deliberate cool charring was never discussed in forest ecology classes with regard to replanting, the focus was more on the forest canopy rather than the soil quality.

So is charring still bad because of the lost canopy?
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posted 13. April 201511:11 AM
No. Charring refers to partially burnt vegetation (small chunks of coal mixes into soil), as opposed to completely burnt ashes(washes/blows away quickly). Smoldering fires in rainforests might singe but don't burn the high canopy. But today they use chainsaws, cut too much, which dries out the forest floor too much, so it burns fast and hot...overkill, canopy weakened or burnt.

We learned about prescribed burning, which burns accumulated fallen dry leaves/branches, which is similar to terra preta, but the purpose was to prevent massive forest fires that do destroy the forest, (the superhot temperatures cook the tree stems through the bark) not to build the soil's fertility.

My point is that I was never trained to distinguish between a burnt forest floor with white ash or black coal, yet there is a big difference in the resulting post-fire soil fertility. The reason it was ignored is because American forestry was based on west European methods (winter snows), not tropical rainforest (high humidity) methods. This is why I study the Congo Pygmies' traditions and language - they've been excellent silviculturalists 'forever', moving their camps around small forest openings, making smoldering fires, etc.

posted 14. April 201509:43 AM
Depends on variables, but they are biochemically the same thing, partially deconstructed tissues of complex carbohydrates and nitrogenous proteins, it all breaks down (completely) to water and mineral ash eventually.

Unlike a compost heap, forest floor detritus rots slowly during the dry season, and can over a period of years accumulate into a thick layer of combustables, posing a danger of hot fires that can quickly climb the canopy and cook the trees.

A hot fire immediately nukes the bonds leaving ash powder, while smoldering fire (hypoxic) bakes & toasts it (vegetal glues (eg. lignin) hold the (cellulose) structure, like bread crust, then charred crust then charcoal). All of these stages (except ash) add a sponge-like quality to the soil, great for water-holding, worm-grub transit, seed implantation & root penetration; while ash just puts minerals on the sun-exposed surface, likely to wash downstream when the rains come back resulting in a hard-pan soil.

Rotting is slow, if the forest floor is covered in leaves, then seeds are slower to penetrate to the soil and are more likely to be eaten or destroyed.

An alternative to cool burning is soil scarification, plowing-mixing the leaves under the topsoil; but this can be costly/difficult.
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